2 research outputs found
Hole Transport Materials with Low Glass Transition Temperatures and High Solubility for Application in Solid-State Dye-Sensitized Solar Cells
We present the synthesis and device characterization of new hole transport materials (HTMs) for application in solid-state dye-sensitized solar cells (ssDSSCs). In addition to possessing electrical properties well suited for ssDSSCs, these new HTMs have low glass transition temperatures, low melting points, and high solubility, which make them promising candidates for increased pore filling into mesoporous titania films. Using standard device fabrication methods and Z907 as the sensitizing dye, power conversion efficiencies (PCE) of 2.94% in 2-μm-thick cells were achieved, rivaling the PCE obtained by control devices using the state-of-the-art HTM spiro-OMeTAD. In 6-μm-thick cells, the device performance is shown to be higher than that obtained using spiro-OMeTAD, making these new HTMs promising for preparing high-efficiency ssDSSCs
TiO<sub>2</sub> Conduction Band Modulation with In<sub>2</sub>O<sub>3</sub> Recombination Barrier Layers in Solid-State Dye-Sensitized Solar Cells
Atomic layer deposition (ALD) was
used to grow subnanometer indium
oxide recombination barriers in a solid-state dye-sensitized solar
cell (DSSC) based on the spiro-OMeTAD hole-transport material (HTM)
and the WN1 donor-Ï€-acceptor organic dye. While optimal device
performance was achieved after 3–10 ALD cycles, 15 ALD cycles
(∼2 Å of In<sub>2</sub>O<sub>3</sub>) was observed to
be optimal for increasing open-circuit voltage (<i>V</i><sub>OC</sub>) with an average improvement of over 100 mV, including
one device with an extremely high <i>V</i><sub>OC</sub> of
1.00 V. An unexpected phenomenon was observed after 15 ALD cycles:
the increasing <i>V</i><sub>OC</sub> trend reversed, and
after 30 ALD cycles <i>V</i><sub>OC</sub> dropped by over
100 mV relative to control devices without any In<sub>2</sub>O<sub>3</sub>. To explore possible causes of the nonmonotonic behavior
resulting from In<sub>2</sub>O<sub>3</sub> barrier layers, we conducted
several device measurements, including transient photovoltage experiments
and capacitance measurements, as well as density functional theory
(DFT) studies. Our results suggest that the <i>V</i><sub>OC</sub> gains observed in the first 20 ALD cycles are due to both
a surface dipole that pulls up the TiO<sub>2</sub> conduction band
and recombination suppression. After 30 ALD cycles, however, both
effects are reversed: the surface dipole of the In<sub>2</sub>O<sub>3</sub> layer reverses direction, lowering the TiO<sub>2</sub> conduction
band, and mid-bandgap states introduced by In<sub>2</sub>O<sub>3</sub> accelerate recombination, leading to a reduced <i>V</i><sub>OC</sub>